There are several projects under way in this laboratory: 1) The pharmacology of glomus (type I) cells studied in tissue slices and in the intact, isolated organ; 2) Further studies on the effects of temperature on the action of different drugs on single chemosensory fibers; 3) The function of single nerve endings of the carotid nerve; and 4) The effect of vasoactive substances on total blood flow and sensory discharge frequency; 1) Glomus cells possess cholinergic receptors. They are depolarized by muscarinic agents, acetylcholine and possibly nicotine. Cell depolarization is accompanied by increased voltage noise when membrane resistance does not change appreciably. 2) Temperature does not affect all stimulating agents in a similar way. The energy of activation (micron) does not change when low pO2, high pCO2, NaCN or ACh increase sensory discharges. However, acid, eserine and haloperidol (a dopaminergic blocker) increase the sensory discharge but micron is reduced. 3) Implement of single sensory nerve endings has revealed the presence of slowly depolarizing "spontaneous" potentials similar to e.p.s.p.'s. At present it is not known whether they represent spontaneous membrane oscillations or produced by leakage of putative neurotransmitters from the glomus cells. 4) Applications of vasoactive substances decrease discharge frequency if the agents induce vasodilatation, accompanied by increased total blood flow. Vasoconstrictors have the opposite effect. The only vasodilator that induces chemosensory excitation is ACh. These experiments should be cautionary to those applying agents such as ACh or dopamine (both vasodilators) in vivo; some of the genuine effects of the drugs may be either masked or enhanced by the vascular effects.